The binding agent feed in the production of fibrous products is realized according to the following methods.
In the fiber formation according to the centrifugal method, a molten jet which is continuously leaving the melt unit is pulled into fibers by means of the centrifugal force of one or more centrifuging wheels. The fibers are conveyed by an air or gas stream acting approximately parallel to the axis of the centrifuging wheels into a subsequent fiber depositing chamber and are aspirated onto an endless wire net conveyor belt which is permeable to air. For the wetting of the fibers with binding agent during fiber blow-off, a fine binding agent spray is sprayed on the fibers according to the so-called spray-type method by means of binding agent nozzles which are arranged in the same plane as the air outlet ducts. Depending on the method, those portions of the melt which are not fiberized, which fall as waste into a conveyor trough located below the disintegrating unit, are wetted with binding agent, so that already at this point, there result considerable binding agent losses.
Furthermore, only a portion of the binding agent entering into the fiber depositing chamber is utilized for the wetting of the fibers, whereas the remaining portion, due to the effect of the aspiration, is transported into the atmosphere or the subsequently coupled filter or cleaning equipment or settles on the parts of the equipment and leads to great fouling of the entire fiber depositing chamber, the transport belt, as well as the suction ducts. Some of the deposits which form on the walls of the fiber depositing chamber become detached again and cause an inferior quality or occlusion of burned spots in the finished products.
Over all, according to experience, the aforementioned binding agent losses amount up to 40% of the quantity used. Besides the increased expenditures for the quantities of binding agent which have to be used, it also results in great environmental pollution, because the binding agents which are used all over the world contain harmful substances, consequently necessitating high expenditures for cleaning equipment in order to reduce the environmental pollution.
The losses are especially high if very thin fiber fleeces are accumulated, such as, for example, in the fiber fleece formation according to the pendulum-type principle or when the product type which subsequently has to be manufactured required these thin fiber fleeces.
In order to reduce the binding agent losses which occur already within the confines of the fiber formation, in some cases, variations of the spraying method are used, wherein binding agent nozzles are arranged inside of the fiber depositing chamber. Our own tests have shown, however, that this very frequently leads to interruptions of the binding agent feed because of fouling of the nozzles, even if corresponding covers are provided, and a further deterioration of the already insufficient ability to control the binding agent distribution in the fiber fleece.
As a second method for the binding agent feed there is known the center-spray-type, whereby a specially constructed, funnel-shaped distributor nozzle is mounted on one of the centrifuging wheels and the feed of the binding agent occurs via a hollow shaft extending through the axis of the centrifuging wheel.
Although this method also avoids the losses due to wetting of components of the melt which are not fiberized and which do not reach the fiber depositing chamber, the other disadvantages of the above-mentioned spray-type method remain in effect in the same way. In addition, there is a high susceptibility to interruptions which makes a widthwise application impossible.
A third method of the binding agent introduction is the so-called wet-type method whereby, after leaving the fiber depositing chamber, the fiber fleece is soaked with binding agent. The wet-type method is predominantly used with equipment whereby the fiber formation occurs according to the blast drawing method which, because of technical reasons, excludes the utilization of the spray-type method for the binding agent feed. In comparison to the other methods, the wet-type method has several advantages (attaining higher binding agent contents, no losses during the introduction of the binding agent, better binding agent distribution). However, it has the disadvantage that it requires for most of the product types a strong dilution of the binding agent in order to assure the desired binding agent contents in the finished products. Because of the necessarily high moisture content in the crude fiber fleece, the energy expenditures for the subsequent drying and curing process and, therefore, also the system-technical expenditures increase many times.
For this reason, the wet-type method is only used with manufacturing equipment of a low throughput performance for the manufacture of particular special products. Additional disadvantages result, furthermore, in that because of the great dilution of the binding agent, there also have to be accepted certain quality reductions as well as a limited choice of binding agents which can be used.